Water is a natural byproduct of the combustion of hydrocarbon or fossil fuels. Permits for water are becoming increasingly difficult to obtain for power plants, which consume relatively large volumes of water during operation. In some cases, the difficulty with obtaining water permits for wells, or use of surface water may preclude construction of a needed power plant. Thus, recovering water from power plants is desirable to obviate the need of obtaining water permits.
Fossil fuel exhaust or flue gas, such as that exhausted from a combustion turbine engine, or downstream of a coal-fired boiler, can contain varying concentrations of water. Water concentration may depend on ambient conditions, fuel composition, inlet air treatment, fuel treatment, flue gas treatment and other factors. If the flue gas exhaust stream were cooled, a portion of that water could be recovered. It is known that cooling an exhaust stream in a condenser to below the precipitation temperature of the moisture in the exhaust gas will result in the condensation of a portion of that moisture. The quantity and percentage of recovered moisture depends on the temperature to which the exhaust can be cooled by the condenser.
Ambient air is commonly the ultimate heat sink for condensers, and the ambient air temperature thus determines the amount of moisture that can be removed by a condenser. In an arid desert environment, for example, the effectiveness of water removal by an ambient air-cooled condenser is limited. Given such high ambient temperatures and the limits of heat exchange equipment, direct condensation alone becomes technically untenable.